Spiral muffler

ABSTRACT

A muffler or silencer having a spiral duct centrally disposed within a housing, with sound absorbent material between the ends of the housing and the ends of the spiral duct to reduce noise.

United States Patent Stemp A 1 Sept. 19, 1972 [54] SPIRAL MUFFLER [72]Inventor: Leslie William Stemp, Ashford, En-

gland [73] Assignee: Cowl Industries Limited, Ontario,

Canada [22] Filed: June 14, 1971 [21] Appl.No.: 152,959

[30] Foreign Application Priority Data June 19, 1970 Great Britain..29,825/7O [52]. US. Cl. ..181/50, 181/66, 181/69 [51] lnt. Cl. ..F0lnl/10, F01n1/12 [58] Field of Search ..181/50, 42, 58, 66, 67-70,181/61-63 [56] References Cited UNITED STATES PATENTS 1,015,698 l/l912Maximw, ..181/50 1,289,856 12/1918 Maxim ..181/66 2,841,235 7/1958Curoni ..181/67 3,018,841 1/1962 Gerlich ..l8l/66 3,563,340 2/1971Duthion ..181/66 FOREIGN PATENTS OR APPLICATIONS 426,769 4/1935 GreatBritain ..181/50 495,576 11/1938 Great Britain ..181/66 829,012 2/1960Great Britain ..181/67 634,222 8/1936 Germany 18 1/66 PrimaryExaminerR0bert S. Ward, Jr. Attorney-Rogers, Bereskin & Parr 57 ABSTRACTA mufi'ler or silencer having a spiral duct centrally disposed within ahousing, with sound absorbent material between the ends of the housingand the ends of the spiral duct to reduce noise.

11 Claims, 7 Drawing Figures Pmmmswwwn 3.692.142

SHEET 1 0F 2 INVENTOR. LESLIE WILLIAM STEMP PATENTEDSEP 9 m2 SHEET 2 0F2 4 INVENTOR. LESLIE WILLIAM STEMP SPIRAL MUFFLER This invention relatestoan improved muffler or silencer for reducing the exhaust noise ofinternal combustion engines, intake noise of compressors and the like.

There is a multitude of muffler designs in current use, and manyconventional mufflers are reasonably efficient. However, there is roomfor improvement in sound attenuation and reduction of back pressure, andthese qualities are not easy to achieve in a muffler of relatively'smallsize.

-Objects of the present inventionare to provide a muffler that hasexcellent sound attenuation characteristics, low back pressure, andrelatively small size.

In a preferred form, the invention consists of a generallycylindricalhousing having generally conical caps at each end, each cap containingsound absorbing material. A spiral duct is positioned in the housing andit has an inner end which communicates with an inlet pipe extending intothe housing through one of said conical caps, and an outer end whichterminates near the wall of the housing. The axis of the spiral duct iscolinear with the axis of the housing. At least one wall of the spiralduct is lined with sound absorbing material. The spiral duct isseparated from each conical cap by means of perforated'platesrespectively positioned at each side of the spiral duct, so that thesound absorbing material in the conical caps is exposed, through theperforations in said plates, to the gas flowing through the spiral duct.The gas is discharged from the mufiler in either of two ways: (a) in oneembodiment, axially, by means of deflectors which direct the gas fromthe outer end of the spiral duct through the other of. said conical capsto an outlet pipe extending axially into said second. conical cap, or(b) in another embodiment, tangentially, by means of an opening formedin the wall of the housing, such opening beingin direct communicationwith the outer end of the spiral duct. I

A preferred embodiment of the invention'is illustrated in'theaccompanying drawing, wherein:

FIG. 1 is a plan view of an improved muffler according to the invention,showing in broken lines some of the internal parts of the muffler; I

FIG. 2 is a sectional view, taken along'the line 8-8 of FIG. 1, showingthe configuration of a spiral duct contained within the housing;

FIG. 3 is a sectional view taken along the line C-C of FIG. 1;

FIG. 4 is a plan view of a bulkhead contained within the housing of FIG.1; 2

FIGS. 5a and 5b are plan views of the perforated plates respectivelyemployed at the upstream and downstream sides of the spiral duct; and

FIG. 6 is a plan view showing the shape of a metal piece used for makinga conical cap.

- Referring to the drawings, and particularly to FIGS. 1 and 2, animproved muffler according to the invention is generally indicated byreference numeral 10, and it includes a housing ll having a cylindricalcentral portion 12 and two end caps 13 and 1.4 of generally conicalshape. A spiral duct '15 is disposed within the central portion 12 ofthe housing 11, and it will be described in greater detail below.

. the outer wall of the outermost turn of the spiral duct An inlet pipe16 extends from the apex of the cap 13 I metal, for example perforatedmild steel sheet having about forty percent (40) open area. The ends ofthe inlet pipe 16 are welded or otherwise securely fastened to the cap13 and to the bulkhead 17, respectively. The bulkhead 17 is formed witha central opening 18 (FIG. 5a which is of the same diameter as thediameter of the inlet pipe 16 and which is aligned therewith. Theinterior of the cap 13 is filled with sound absorbing material 19 suchas rock wool.

' The axis of the spiral duct 15 is coaxial with the axis of the housing11, and its width is equal to the'width of the central portion 12 of thehousing 1 l. The inner end of the spiral duct 15 is open and is disposedat thecenter of the housing 11; it is in communication with the innerend of the inlet pipe 16..The radius of the spiral duct initially isequal to the radius of the inlet pipe 16, but the radius increasessmoothly from the inner end of the spiral ductlS to the outer endthereof. The outer end of'the metal sheet from which the spiral duct 15is formed is curved inwardly and is secured to 15, as shown at 20, thusforming a cylindrical surface which constitutes the central portion 12of the housing 11. The spiral duct may be constructed from a pluralityof semicylindrical plates fastened together by any suitable means, orfrom a single piece of sheet metal. T he inner end of the duct 15terminates in a short bent portion 21, the bight portion of whichprovides a smooth surface against which the incoming gases flow as theyenter the spiral duct 15. The bent portion 21 also pro.- vides aconvenient anchor point for one end of a lining 22 which covers one wallof the spiral duct 15, and for one end of a perforated or expanded metalsheet 23, represented in FIG. 2 by broken lines, which keeps the lining22 in place against the wall of the spiral duct 15. The width of themetal sheet 23 is the same as that of the spiral duct 15. The lining 22may be of any suitable sound absorbing material capable of withstandingthe temperature and forces to which it is subjected, such as rock wool.

Although the lining 22 is shown as attached to only one wall of thespiral duct 15, it will be understood that both walls of the spiral duct15 could be lined, if desired. However, it has been found that goodresults may be obtained if the lining is applied to the wall shown,which is on the low pressure side of the gas stream flowing through thespiral duct 15. Similarly, although a perforated sheet 23 is shown forkeeping the lining 22 in place, it will be understood that if the lining22 is of woven material or is otherwise of unitary construction, thelining 22 may be attached to the spiral duct 15 by means of clips,rivets, etc., or it may be formed into a long sheath into which themetal sheet forming the spiral duct 15 may be inserted. Alternatively,the lining may be formed in tubular shape so that it takes the form ofthe spiral duct 15 itself.

In the embodiment of the invention shown in the drawings, the gasesemerge from the muffler axially, and this is accomplished as follows.The gases approaching the outer wall of the central portion 12 of thehousing 11 are directed in an axial direction by means of severaldeflectors 24 towards a bulkhead 25. The bulkhead 25 is similar to thebulkhead 17, except that insteadof having a central opening 18, thebulk- .head 25 has a wide peripheral notch 26 through which the gasesenter the end cap 14. A smaller bulkhead 27 is fixed inside the end cap14 downstream from the bulkhead 25, and it has a similar notch 28aligned with the notch 26. A channel-shaped plate '29 bridges thenotches 26 and 28 of the bulkheads 25 and 27 and provides a passage wayfor the gases betweenthe spiral duct 15 and an expansion chamber 30located downstream from the bulkhead 27. An outlet pipe 31 is secured tothe end cap 14 at the apex thereof, and communicates at its inner endwith the expansion chamber 30, so that gases leave the muffler axiallythrough the outlet pipe 31.

The spiral duct may be spot welded to the bulkheads 17 and 25, oralternatively spiral grooves may be formed in the bulkheads l7 and forreceiving the edges of the spiral duct 15. The shape of the spiral duct15 is also largely a matter of choice; for example, the cross-section ofthe spiral duct 15 may be rectangular (when viewed at right angles tothe axis of the 'mufiler 10), square or circular. The length of thecentral portion 12 of the housing 11 can also be varied, and may eitherbe less or greater than its diameter. However, for best results thespiral duct 15 should have at least about two and one-half turns; moreturns would provide greater sound attenuation at the possible expense ofsomewhat greater back pressure. The distance between the walls of theduct (hereinafter called duct width) is shown in FIG. 2 as beingsubstantially constant, but this is also a matter of choice and could bemodified if desired. For example, the duct width could increase from theinner end of the spiral duct 15 to the outer end; this would give ashorter duct length for a given diameter, and lower back pressureatthejpossible expense of noise attenuation. Conversely if the ductwidth decreased outwardly, the duct would be longer for a givendiameter, and the noise attenuation would likely be somewhat improved,at the possible expense of back pressure.

Instead of discharging the gases into the expansion chamber 30, it ispossible to extend the channel shaped plate 29 to the inner end of theoutlet pipe 31. In this case, the plate 29 would be shaped so that itwould provide a smooth enclosed duct for conveying the gases from thespiral duct 15 to'the outlet pipe 31, with no rapid expansion asprovided by the expansion chamber 30. This arrangement may result insomewhat less back pressure.

The construction of the mufi'ler could be simplified considerably andthe back pressure reduced still further by removing the gasestangentially from the outside of the central portion 12 of the housing11, instead of through the outlet pipe 31. This is easily accomplishedby merely forming an elongated opening in the periphery of the centralportion 12 of the housing 11, for example in the region of thedeflectors 24 of the embodiment shown in FIG. 1.

What I claim is:

1. Apparatus for silencing an engine and the like, comprising:

a. a housing having an inlet and an outlet, a side wall,

two end walls, and a longitudinal axis,

b. a spiral duct in said housing, said spiral duct having opposed ends,said spiral duct being positioned with its longitudinal axis parallelwith the longitudinal axis of the housing, the ends of said spiral ductrespectively being spaced inwardly from the end walls of the housing,said spiral duct having an inlet and an outlet,

c. first 'duct means for conveying gases from the inlet of the housingto the inlet of the spiral duct,

. second duct means for conveying gases from the outlet of the spiralduct to the outlet of the housing, and

e. sound absorbent material substantially filling the spaces between theends of the spiral duct and the ends of the housing.

2. Apparatus as claimed in claim 1 wherein there are first and secondspaced-apart, parallel bulkheads in said housing, said bulkheads beingpositioned to define a first compartment adjacent to one end wall of thehousing, a second compartment adjacent to the first compartment, and athird compartment between the second compartment and the other of saidend walls of the housing, said bulkheads having a plurality of openingsthrough which gases may freely pass, said spiral duct being positionedin said second compartment and said sound absorbent material beingplaced in said first and third compartments.

3. Apparatus as claimed in claim 2 wherein the inlet of the spiral ductis adjacent to the longitudinal axis of the housing, wherein the housinginlet and outlet are respectively positioned in the end walls of thehousing, and wherein the second bulkhead is formed with an openingthrough which gases passing through the spiral duct outlet may enter thethird compartment.

4. Apparatus as claimed in claim 2 wherein the side wall of the housingis cylindrical and encloses the second compartment, and the end walls ofthe housing are conical and respectively enclose the first and thirdcompartments.

5. Apparatus as claimed in claim 2 wherein the bulkheads are formed ofperforated metal sheet.

6. Apparatus as claimed in claim 2 wherein at least one wall of thespiral duct is lined with sound absorbent material.

7. Apparatus as claimed in claim 3 wherein there is a third bulkhead inthe third compartment, the third bulkhead being positioned between thesecond bulkhead and the outlet, the third bulkhead forming one wall ofan expansion chamber that is in communication with and positionedbetween the outlet of the housing and the third compartment.

8. Apparatus as claimed in claim 7 wherein the first bulkhead has acentral opening, and wherein the first duct means comprises a pipe thatis connected between the inlet of the housing and said central opening.

9. Apparatus for silencing an engine and the like, comprising:

a. a housing having an inlet and an outlet, a side wall and two endwalls,

b. a spiral duct in said housing, said spiral duct having an inlet andan outlet,

c. first duct means for conveying gases from the inlet of the housing tothe inlet of the spiral duct,

d. second duct means for conveying gases from the outlet of the spiralduct to the outlet of the housing, and

e. sound absorbent material secured to at least one wall of said spiralduct and extending substantially the entire length of said spiral duct.

6 10. Apparatus as claimed in claim 9, wherein said length of saidspiral duct. sound absorbent material is applied to a wall of said 11.Apparatus as claimed in claim 9, wherein all spiral duct which is on thelow r r id f th inner surfaces of said spiral duct are lined with saidgases flowing through the spiral duct, and said sound Sound absorbentmammalabsorbent material extends substantially the entire 5

1. Apparatus for silencing an engine and the like, comprising: a. ahousing having an inlet and an outlet, a side wall, two end walls, and alongitudinal axis, b. a spiral duct in said housing, said spiral ducthaving opposed ends, said spiral duct being positioned with itslongitudinal axis parallel with the longitudinal axis of the housing,the ends of said spiral duct respectively being spaced inwardly from theend walls of the housing, said spiral duct having an inlet and anoutlet, c. first duct means for conveying gases from the inlet of thehousing to the inlet of the spiral duct, d. second duct means forconveying gases from the outlet of the spiral duct to the outlet of thehousing, and e. sound absorbent material substantially filling thespaces between the ends of the spiral duct and the ends of the housing.2. Apparatus as claimed in claim 1 wherein there are first and secondspaced-apart, parallel bulkheads in said housing, said bulkheads beingpositioned to define a first compartment adjacent to one end wall of thehousing, a second compartment adjacent to the first compartment, and athird compartment between the second compartment and the other of saidend walls of the housing, said bulkheads having a plurality of openingsthrough which gases may freely pass, said spiral duct being positionedin said second compartment and said sound absorbent material beingplaced in said first and third compartments.
 3. Apparatus as claimed inclaIm 2 wherein the inlet of the spiral duct is adjacent to thelongitudinal axis of the housing, wherein the housing inlet and outletare respectively positioned in the end walls of the housing, and whereinthe second bulkhead is formed with an opening through which gasespassing through the spiral duct outlet may enter the third compartment.4. Apparatus as claimed in claim 2 wherein the side wall of the housingis cylindrical and encloses the second compartment, and the end walls ofthe housing are conical and respectively enclose the first and thirdcompartments.
 5. Apparatus as claimed in claim 2 wherein the bulkheadsare formed of perforated metal sheet.
 6. Apparatus as claimed in claim 2wherein at least one wall of the spiral duct is lined with soundabsorbent material.
 7. Apparatus as claimed in claim 3 wherein there isa third bulkhead in the third compartment, the third bulkhead beingpositioned between the second bulkhead and the outlet, the thirdbulkhead forming one wall of an expansion chamber that is incommunication with and positioned between the outlet of the housing andthe third compartment.
 8. Apparatus as claimed in claim 7 wherein thefirst bulkhead has a central opening, and wherein the first duct meanscomprises a pipe that is connected between the inlet of the housing andsaid central opening.
 9. Apparatus for silencing an engine and the like,comprising: a. a housing having an inlet and an outlet, a side wall andtwo end walls, b. a spiral duct in said housing, said spiral duct havingan inlet and an outlet, c. first duct means for conveying gases from theinlet of the housing to the inlet of the spiral duct, d. second ductmeans for conveying gases from the outlet of the spiral duct to theoutlet of the housing, and e. sound absorbent material secured to atleast one wall of said spiral duct and extending substantially theentire length of said spiral duct.
 10. Apparatus as claimed in claim 9,wherein said sound absorbent material is applied to a wall of saidspiral duct which is on the low pressure side of the gases flowingthrough the spiral duct, and said sound absorbent material extendssubstantially the entire length of said spiral duct.
 11. Apparatus asclaimed in claim 9, wherein all inner surfaces of said spiral duct arelined with said sound absorbent material.